I got an used autopilot for my Catalina 27 (wheel). I don't have a dedicated switch on my fuse panel for my instruments. I will add that in the near future when I replace the non working depth and speed. Today I installed the autopilot and wanted to put it on a switch in the cockpit. I have attached a photo of the switch. I am running directly from the battery to the switch, then off the switch to the control head, with a fuse inline. I connected the negative to the battery and then connected the positive. All worked as it should, except I realized the switch was in the on position. I flipped the switch off and went to put the positive back on and it created a large spark. It then removed the negative, installed the positive and tried to install the negative and had the same issue. The ring terminal even tried to weld to the battery post.

Um, you just wired that switch to short circuit your battery with no fuse. That is very dangerous, remove it immediately, get new wires and a new switch, and read how to wire the switch properly. Don Casey has a good boat electrics book.

I got an used autopilot for my Catalina 27 (wheel). I don't have a dedicated switch on my fuse panel for my instruments. I will add that in the near future when I replace the non working depth and speed. Today I installed the autopilot and wanted to put it on a switch in the cockpit. I have attached a photo of the switch. I am running directly from the battery to the switch, then off the switch to the control head, with a fuse inline. I connected the negative to the battery and then connected the positive. All worked as it should, except I realized the switch was in the on position. I flipped the switch off and went to put the positive back on and it created a large spark. It then removed the negative, installed the positive and tried to install the negative and had the same issue. The ring terminal even tried to weld to the battery post.

What am I doing wrong?

Looks like you have both positive and negatives on the switch - in the on position a dead short. Switches only control the positive wire. The only time a negative is used on a switch is if it has an indicator light that needs it.

You should have the negative going to the autopilot. The positive goes to to one side of the switch and from the other side to the autopilot. Fuse the positive close to the battery.

I got an used autopilot for my Catalina 27 (wheel). I don't have a dedicated switch on my fuse panel for my instruments. I will add that in the near future when I replace the non working depth and speed. Today I installed the autopilot and wanted to put it on a switch in the cockpit. I have attached a photo of the switch. I am running directly from the battery to the switch, then off the switch to the control head, with a fuse inline. I connected the negative to the battery and then connected the positive. All worked as it should, except I realized the switch was in the on position. I flipped the switch off and went to put the positive back on and it created a large spark. It then removed the negative, installed the positive and tried to install the negative and had the same issue. The ring terminal even tried to weld to the battery post.

What am I doing wrong?

You wired a dead short!!!!

A switch is intended to OPEN/BREAK a positive wire and gets inserted into the positive wire (would do the same on negative but in the US we open positive)..

You wired a dead short by connecting battery B+ to battery B- when the switch is made....

ANY WIRES CONNECTED TO THE BATTERY NEED A FUSE WITHIN 7", OR AS CLOSE AS POSSIBLE, TO THE BATTERY + TERMINAL!!!!

Time to get Charlie Wings book, Boatowners Illustrated Electrical Handbook - Second Edition

It looks like you're in way, way over your head on electronics. I say this without judgement - it can be hard to know what you don't know when you're a novice - but wiring a switch is about as basic as things get. You probably should stop before something catches fire, and find a way to learn more about DC electronics. I'd suggest some automotive wiring; at least if your car catches fire (mine did!) you can walk home.

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